1. Field of the Invention
The present invention generally relates to a method of and an apparatus for restricting a copy or duplication of digital information such as digital video image etc., and also an apparatus for recording the digital information. More particularly, it relates to the method of and the apparatus for restricting the copy of the digital information and also the apparatus for recording the digital information, in which a copy generation of the digital information is managed by using a watermark.
2. Description of the Related Art
A digital transmission of a video image is being generalized by a realization of a digital television broadcast. A recording apparatus, which digitally records the video image onto an optical disc or magnetic tape, is also being diffused. If the video image can be digitally recorded, it is possible to copy or duplicate the video image without deterioration of the quality of the video image. Therefore, it is necessary to restrict a copy of a video image from a view point of a copy right and the like.
A watermark (i.e., an electronic watermark) technique is one of techniques for restricting the copy of the video image. The watermark technique is a technique for burying or inserting the information related to the copy restriction into the digital video image. Hereinafter, the information related to the copy restriction to be buried into the digital information is called as a “watermark”. The watermark is buried in the video image so as to be hidden in the video image. Thus, even if the a watermark is buried, the quality of the video image is hardly deteriorated. Since a person, who has received the video image in which the watermark is buried, cannot recognize even an existence of the watermark in the video image, it is very difficult for him or her to remove the watermark from the video image.
When the digital video image is inputted into the recording apparatus, the recording apparatus firstly judges whether or not the watermark exists in the video image. If the watermark does not exist, the recording apparatus judges or determines that the video image is copy-allowed, and records the video image onto an optical disc for example. On the contrary, if the watermark exists, the recording apparatus judges that there is some kind of copy restriction for the video image, and does not record the video image for example. In this manner, it is possible to restrict the copy of the digital video image by the existence and absence of the watermark.
By the way, in order to solve the problem of the copy right while diffusing the digital television broadcast generally, it is necessary not only to allow or prohibit the copy of the digital video image but also to manage a generation of the copy (i.e., the number of times of the copy). For example, if it is possible to allow copying the digital information transmitted from a broadcast station just at a first generation by the recording apparatus and to prohibit copying at a second or more than second generation (i.e., to allow copying the digital information only once) for example, the receiver of the television broadcast can watch the transmitted video image by recording it without being restrained on the broadcast time, and at the same time the problem of the copy right can be solved.
In order to realize this kind of generation management of the copy of the digital video information by use of the aforementioned watermark, it is required to prepare one watermark indicating to prohibit copying and another watermark indicating to allow copying at a first generation. Further, it is required to make the recording apparatus recognize these two kinds of watermarks. Furthermore, it is required to change the watermark when recording the digital video information which is copy-allowed only at the first generation, the digital video image after recording is treated as the digital video image which is copy-prohibited or protected.
However, it is required to bury the watermark into or under the video image so that a person watching the video may not notice the existence of the watermark while restraining the deterioration of the quality of the video image. In order to satisfy these requirements, the structure of the watermark itself is limited in certain degrees. As a result, there is a problem that it is certainly difficult to prepare a plurality of kinds of watermarks and it is also difficult to change the watermark.